Two new studies attempt to prove the Giant Impact Theory in different ways

Two different studies say they've found evidence supporting the theory that the moon was created from a collision between Earth and a Mars-sized body.

The Giant Impact Theory, which was proposed back in 1975, suggests that the early Earth and a Mars-sized planet called Theia collided with one another. This completely obliterated Theia, and its composition created a ring around Earth and eventually came together to create the moon.

While scientists have been able to explain how this event occurred, one major thing didn't add up: the composition of the moon.

Scientists long believed that for this theory to be true, the moon would have to be composed mainly of Theia's elements. Moon rocks from that were brought to Earth were studied, and surprisingly, they had the same types and amounts of elements that the Earth had, including titanium, silicon and oxygen. This didn't make sense, and has left the theory wide open for the last 30+ years.

However, scientists from Washington University in St. Louis managed to measure a small excess of a heavier variant of zinc in moon rocks from that were brought to Earth in the 1970s. They believe the excess is due to heavier zinc atoms condensing out of the collision's cloud faster than the lighter zinc atoms, and the vapor that remained escaped before it condensed.

This bit of sorting by mass is called isotopic fractionation, and it's what scientists have been looking for all along. This shows that the moon rocks were depleted of easily evaporated elements called volatiles, and a large collision could explain this depletion while other theories can't.

"The magnitude of the fractionation we measured in lunar rocks is 10 times larger than what we see in terrestrial and Martian rocks," said Frédéric Moynier, PhD, from Washington University in St. Louis. "So it's an important difference."

But the Washington University team isn't the only one to bring new evidence to the table. Robin Canup, a planetary scientist from the Southwest Research Institute Colorado, used Harvard scientists' findings to create a theory of her own related to the collision.

According to the Harvard team, which used computer simulations to create its theory, ancient Earth had to have been spinning too fast for today's 24-hour rotation. They suggested that early Earth and a body half the size of Mars could have collided where both were obliterated and combined elements to create both the moon and Earth's heavy iron core/lighter rock layers.

At a later point, Earth's rotation could have slowed due to the moon and sun aligning in a way that changed Earth's orbit.

Canup used the idea that Earth's rotation was slowed and came up with the theory that two bodies similar in size collided at a slow speed, and their materials merged to create the Earth and moon.

If two planets could form in an area of the accretion disk near enough to each other that they would eventually collide, why would their composition be different enough that we would be able to tell if there was a through mixing of the debris or not?

Two similar size planets forming from the same material should be nearly the same in composition unless one forms much earlier than the other. As for the lighter Zinc atoms being missing from the moon, did they take into consideration the lower atmospheric pressure and the higher degree of solar and cosmic radiation hitting the surface which could have caused the lighter isotope to be in a lower concentration? There are a lot of variables between what a rock on Earth and a rock on the Moon would have been exposed to between the time they formed and the time when man finally got there to take a sample. Unless you are looking at some fairly deep core samples from the Moon that is.

"Nowadays, security guys break the Mac every single day. Every single day, they come out with a total exploit, your machine can be taken over totally. I dare anybody to do that once a month on the Windows machine." -- Bill Gates